This invention relates generally to a system and method for differentiating material characteristics using an imaging system and more particularly to a system and method for differentiating material characteristics using a hybrid x-ray detector.
Energy discrimination adds significantly to the capabilities of an x-ray imaging detector. Energy discrimination improves signal to noise and potentially allows different materials to be distinguished. Current energy discrimination applications are limited to radiography (RAD) (digital radiography and computed radiography), mammography, and some dual energy computed tomography products. One strategy is to separate two detectors with a thin plate of metal, which preferentially absorbs low energy x-rays. Low energy x-rays then provide a relatively larger signal to the first detector and higher energy x-rays provide a relatively larger signal in the second detector. Another approach is to have two separate x-ray exposures and using different x-ray spectra for each. These approaches have in common that multiple images are acquired sequentially, and combined to produce one or more processed images representing the additional energy information. However, this approach only works well for single shot exposures, such as in RAD and mammographs.
For cardiac imaging, it is desirable to image small objects, such as guide wires and catheters, which are moving in real time, and to do so in thick patients, for which image quality is a major challenge. For this type of imaging, both high spatial resolution and sensitive material discrimination are desirable. Catheters are becoming smaller and harder to visualize in the rapidly moving heart. Thus, sequential imaging approaches to energy discrimination are not suitable for this application.
It is also noted that there also exist direct conversion detectors, such as thin film direct conversion detectors and single crystal direct conversion detectors. Thin film direct conversion detectors typically consist of polycrystalline materials, which are not capable of energy discrimination. Single crystal direct conversion detectors are more expensive to produce and are only available in small sizes. They typically have poor performance at the high x-ray flux rates required, and the small size requires tiling to produce large areas, which can result in gaps between tiles. The gaps cause data to be absent from the image, and can result in a misdiagnosis if critical anatomy is not correctly imaged.